Orthodontic appliances or "braces" are common devices employed by orthodontists to correct or enhance tooth movement and growth in the human patient. Orthodontic appliances are typically attached to the tooth or teeth to be moved and corrective forces are applied to the appliance by means of springs, elastics, and other devices known in the art.
The mechanism by which mechanical ortho appliances function is fairly straightforward. Force is applied in the direction towards which it is desired to have tooth movement. Initially, spaces around the teeth and the elastic nature of the epithelial gingiva surrounding each tooth allow for considerable movement on the order of about 0.5 to about 1 mm. At this point, the tooth becomes compressed against the mandibular or maxillary bone. As the force continues to be applied, compressed bone cells undergo osteoclasty, i.e., bone re-absorption, and bone cells filling in the gap created by and behind the tooth movement undergo osteoblasty, i.e., bone growth. These processes are typically observed as tooth movement, followed by a lag time, followed again by tooth movement and so on until the ortho force is halted when the desired repositioning has occurred.
While these traditional, mechanical ortho appliances and techniques are generally effective, there are several deficiencies and drawbacks in their use. For example, mechanical ortho appliances generally require a wearing time on the order of several years with forces being changed every few weeks. In addition, ortho appliances are often cumbersome and uncomfortable. Given the length of time certain appliances must be worn, such discomfort can be substantial and prolonged.
It is desirable in the art to reduce the lag time present in ortho movement and thereby decrease the time necessary for a patient to wear an ortho appliance. Korostoff and Davidovitch disclosed in United States Patent No. 4,153,060, "Method and Apparatus for Electrically Enhanced Bone Growth and Tooth Movement," the feasibility of using electrical orthodontics to decrease the overall time required to move a tooth orthodontically. Korostoff and Davidovitch demonstrated that, by using an electric stimulation with an ortho force, the overall time required to move a tooth orthodontically could be reduced significantly. In addition, such electric stimulation techniques could potentially be used for correcting other oral bone growth malformations, such as cleft pallet.
While the methods in the prior art have great promise, one major difficulty and deficiency has been poor biocompatibility of the stimulating electrodes. Biocompatibility at the interface between stimulating electrodes and the tissue with which the electrodes are in contact, is desirable for meaningful use of electro-stimulating ortho appliances. Poor biocompatibility of the electrodes in orthodontic appliances results in severe lacerations, ulcerations, irritation and swelling of the epithelial gingiva.
Attempts in the prior art to use noble metal electrodes, such as gold, silver, platinum, palladium, as well as stainless steel, proved to lack biocompatibility. Moreover, attempts in the prior art to utilize a gel interface between the electrode and the tissue using, for example, agar and agar solutions, yielded a similar lack of biocompatibility.
Noble metal electrodes used with an agar gel interface were found to deteriorate under use. For example, U.S. Pat. No. 4,570,637 of Gomes and Massione discloses that silver electrodes using an electrically conductive gel, such as an agar solution of sodium chloride, when subjected to DC current, are ionized and the silver is converted to silver chloride. This conversion causes an increased resistance and renders the electrode useless for biomedical purposes. In addition, experiments indicate that noble metals, such as silver, when ionized, migrate across such agar gel interfaces and react adversely with the gingiva.
The present invention overcomes many of the disadvantages inherent in the methods of electric stimulation of tissues described above by providing a biocompatible anode and a biocompatible cathode for use in orthodontic electroosteogenesis, particularly where relatively high electric currents are employed. The present invention significantly reduces gingival irritation, such as tissue laceration, and increases appliance wearability and patient comfort.